In this paper, we present a general review of the development of a high-power all-fiber side-pumping combiner developed over the past few years. Our main focus is on the fundamental mechanism of operation, in addition to a review of the development and the challenges associated with the realization of a functional side-pumping combiner, which was fabricated using a tapered-fused technique. This technique can potentially be exploited as a side-pumping method because of its high coupling efficiency, high signal transfer efficiency, and its capability of handling high pump powers up to the kilowatt range. This review includes an overview of theoretical and experimental results, the challenges associated with fabrication, an investigation of the loss mechanism, and an overview of the performance improvement of the combiner. In summary, a new (2+1) ×1 side-pumping combiner for a 2.5 kW fiber laser based on tandem pumping is introduced. The presented results suggest that the side pumping combiner has a high power loading capability as well as a high coupling efficiency when applied in a tandem-pumping scheme, due to the high brightness of the fiber laser as the pump light source.